[Preliminary Simulation Results on Power Saving] Date: 2009-11-19 Authors: Slide 1 1

Abstract This presentation reports the preliminary results of our simulations of existing power saving mechanisms. The scenario simulated is taken from IEEE 802 Doc 09/0161r02, Usage Model 2d: Wireless Networking for Office. The performance and effect of APSD have been examined. Slide 2

Simulation Scenario* Pre-Conditions: Office with people engaged in high quality/high revenue services that involve video and voice interaction with client and transferring large volumes of multimedia data. A single AP serves 5 people. The office comprises 5 – 500 people. Application: Multiple applications run at the same time. High definition compressed video uses something like an Blu-ray codec. Voice is standard definition quality using a codec like G729. Aggregate bandwidth requirement is 5 simultaneous video streams per AP. Voice requirements are: ~50Kbps, Jitter <30msec. Delay <30msec. 1.0E-1 PER. Environment: Mostly not Line of sight within a single office. People walking around the office. There is potentially unmanageable interference from neighboring offices within 100 feet (horizontally) or adjacent floors (vertically) when in 2.4 / 5 GHz. AP density is more than 1 AP per 40m X 40m Traffic Conditions (per AP): 2 WLAN video streams 2 WVoIP streams Up to 5 best effort data streams The best effort data traffic can take up to 20% of the available bandwidth with saturated offered load. Use Case: Users run different applications during the day and may start each application at different time. A typical sequence is starting up a voice call, adding video sending/receiving multi-media data and discussing this over the voice/video link The duration of such a use case is typically one hour. Up to three of these “sessions” per AP may be going on in parallel. * This was taken from Doc 09/0161r02, Usage Model 2d: Wireless Networking for Office Slide 3

Network Topology Slide 4

Traffic Pattern Slide 5 Flow No. STAs (Source/Sink) Source Location (meters) Sink Location (meters) Channel Model Application (Forward Traffic / Backward Traffic) Application Load (Mbps) (Forward / Backward) Rate Distribution (Forward / Backward) MSDU Size (B) (Forward / Backward) Max. Delay (ms) (Forward / Backward) Max. PLR (Forward / Backward) 1 AP / STA1 (0,0) (0,5) C VoIP / VoIP 0.008 / 0.008 UDP / UDP 20/ 20 30 / 30 5% / 5% 2 AP / STA2 (-10,-10) 3 AP/ STA3 (5,0) 4 STA3/ AP Local file transfer Max. 1Gbps TCP 300 INF N/A 5 AP/ STA 4 (-7,7) 6 STA 4/ AP Blu-ray/ control channel 50.00 / 0.06 Constant, UDP / Constant UDP 1500 / 64 20 / 100  10^-7 / 10^-2 7 STA 5/ AP (10,5) 8 Slide 5

Simulation Parameters Bit rate for DATA packets 500 Mbps Bit rate for RTS/CTS/ACK 6 Mbps aCWmin 31 aCWmax 1024 PLCPDataRate A Slot Time 9 us SIFS 16 us DIFS 34 us PreambleLength 144 bits PLCPHeaderLength 48 bits MAC header 224 bits IP header 160 bits DATA packet Payload size + MAC header + IP header=Payload size+ 384 bits RTS CTS, ACK 112 bits AC 3 for VoIP traffic PF 2, AIFS 2, CW_MIN 7, CW_MAX 15 AC 2 for Video traffic PF 2, AIFS 2, CW_MIN 15, CW_MAX 31 AC 0 for Video Best effort traffic PF 2, AIFS 7, CW_MIN 31, CW_MAX 1023 The simulation runs on ns2 platform. Slide 6

Performance without Aggregation Network Performance with APSD Delay (ms) Throughput (Kbps) Packet Loss (%) Uplink Downlink VoIP 0.361 10.622 8 Video 326.813 0.661 19,298 60 60.23 TCP 18.668 N/A 998.198 Network Performance without APSD Delay (ms) Throughput (Kbps) Packet Loss (%) Uplink Downlink VoIP 0.375 0.351 8 Video 304.989 0.619 19,907 60 59.06 TCP 22.137 N/A 1,068.31 Note the data here are average numbers over 4 VoIP sessions, 2 Video sessions and 2 TCP sessions. Slide 7

802.11n Capacity with Video traffic Contention Window PLCP Header Video Frame DIFS SIFS Ack 34 µs 67 µs (min average) 28 µs 16 µs 32 µs Time 1. Video Frame = (Data + IP header + MAC header)/DataRate ( 1500 + 20 + 28 ) * 8 / 500 = 24.768 µs 2. Require Bandwidth = Application Load * Frame Start Interval / Video Frame 50 * (34+67+28+24.768+16+32) / 24 = 420.315 Mbps 3. Number of Video uplink sessions = Bandwidth * Utilization / Require Bandwidth 500 * 0.8 / 420.315 = 1.05 Reference: IEEE 802.11-07/2704r00, Efficiency of VoIP on 802.11n Slide 8

Data Aggregation In order to support the given traffic load, Aggregated MSDU is used. In the results after this slide, four video MSDUs are aggregated into one A-MSDU. VoIP and TCP packets are not aggregated. Slide 9

APSD Power Saving Effect STA 1 (VoIP only) STA 2 STA 3 (VoIP, TCP) STA 4 (VoIP, Video) STA 5 Slide 10

VoIP Traffic Delay with and w/o APSD STA 1 (VoIP only) STA 2 STA 3 (VoIP, TCP) STA 4 (VoIP, Video) Note: Jitter for VoIP traffic with APSD is < 2 µs, and <0.1 µs without APSD Slide 11

Video Traffic Performance Uplink w/ APSD Downlink w/o APSD Slide 12

APSD’s effect on TCP throughput STA3 (VoIP, TCP) STA5 (Video, TCP) Note: all TCP traffic is uplink traffic Slide 13 13

Delay Comparison for all Traffic Types VoIP Video TCP Note: 1) the data here are average numbers over 4 VoIP sessions, 2 Video sessions and 2 TCP sessions. 2) there is no data collected for downlink TCP traffic so the data is not available. Slide 14

Summary and Future Works A single stream of 500Mbps cannot support the given traffic load. Aggregation gets the job done. APSD allows STAs sleep >95% of the time for VoIP traffic in this specific scenario; APSD increases the delay for downlink VoIP traffic (from <1ms to ~10ms), but still within the requirement (<30ms). APSD slightly increases the delay for video traffic when it is running in the AP. TCP delay is >20% larger, and throughput is about 10% lower when APSD is running. Future work Run the simulation for PSMP (simulator is ready) Develop module to support direct links so that STA to STA traffic can be simulated. Support multiple streams (receivers) Enhanced MAC functions needed. Slide 15